Ch. 3 TEXT 13

yajna-sistasinah santo
mucyante sarva-kilbisaih
bhunjate te tv agham papa
ye pacanty atma-karanat

TRANSLATION

The devotees of the Lord are released from all kinds of sins because they eat food which is offered first for sacrifice. Others, who prepare food for personal sense enjoyment, verily eat only sin.

Srila Bhaktivedanta Svami Prabhupada’s PURPORT

The devotees of the Supreme Lord, or the persons who are in Krsna consciousness, are called santas, and they are always in love with the Lord as it is described in the Brahma-samhita: premanjana- cchurita-bhakti-vilocanena santah sadaiva hrdayesu vilokayanti. The santas, being always in a compact of love with the Supreme Personality of Godhead, Govinda (the giver of all pleasures), or Mukunda (the giver of liberation), or Krsna (the all-attractive person), cannot accept anything without first offering it to the Supreme Person. Therefore, such devotees always perform yajnas in different modes of devotional service, such as sravanam, kirtanam, smaranam, arcanam, etc., and these performances of yajnas keep them always aloof from all kinds of contamination of sinful association in the material world. Others, who prepare food for self or sense gratification, are not only thieves, but are also the eaters of all kinds of sins. How can a person be happy if he is both a thief and sinful? It is not possible. Therefore, in order for people to become happy in all respects, they must be taught to perform the easy process of sankirtana-yajna, in full Krsna consciousness. Otherwise, there can be no peace or happiness in the world.

Prabhuji talking about prasada and what one should eat in darsana with a devotee:

The sinful food you eat destroys you. Take prasada. Everything else you eat is sin. If you cook for yourself, according to what you like, Krsna says, that is sin. What you cook for others, offer, then serve to others, and take the remnants, that is prasada.